The present invention is generally in the field of analog-to-digital converter systems. More specifically, the invention is in the field of optically clocked optoelectronic track and hold devices in analog-to-digital conversion systems.
Signal processing is the analysis and/or modification of sensory information. Signal processing applications include space photograph enhancement, medical diagnostic imaging (e.g., CT, MRI and ultrasound), movie special effects, telephone voice and data compression, speech recognition, radar, sonar, oil and mineral prospecting and earthquake recording and analysis. Most signal processing applications receive sensory data from real-world phenomena (e.g., sound waves, seismic vibrations and RF waves) as analog signals. Signal processing systems typically convert analog signals to digital signals using analog-to-digital converters for processing by digital signal processing (“DSP”) systems.
A typical analog-to-digital converter (ADC) receives an analog input signal and a clock signal and outputs a digital signal comprising a discrete sequence of measured values, which represents the analog input signal measured at time intervals that are based on the clock signal. A typical ADC includes an electronic track and hold (“TH”) device and a quantizer. A diode bridge circuit is commonly used in TH devices. An electronic TH device receives an electronic clock signal that switches the electronic TH device from a track mode to a hold mode via electronic switches. When operating in track mode, the electronic TH device continuously measures an analog signal. When operating in hold mode, the electronic TH device holds the measured value of the analog signal. The quantizer assigns measured values to multiples of a basic unit.
Disadvantageously, electronic TH devices switch slowly due to slow rise times of electronic clocking, resulting in a relatively long aperture time (i.e., the time for the track-to-hold transition). In addition, electronic clock signals suffer from aperture jitter (i.e., error in the timing of the initiation of the track-to-hold transition) due to clock inaccuracies. Further, electronic clock signals can disadvantageously interfere with analog input signals (e.g., cross talk).
Therefore, a need exists for track and hold devices that can quickly switch between track mode and hold mode. In addition, a need exists for track and hold devices that reduce aperture jitter. Further, a need exists for track and hold devices that reduce interference with analog input signals.